Sound barrier

ABSTRACT

A sound barrier comprising a plurality of hollow, wedge-shaped, energy dissipating cells mounted in parallel, side-by-side, spaced relationship as inverse-acting acoustic horns, first sides of all cells being coplanar. Each of the cells has a plurality of openings in the remaining two sides thereof along the edges which are adjacent the first side and a plurality of elongated openings along the apex defined by the intersection of the two sides. Each cell is made in two interlocking parts, one part forming the first side and the other part forming the remaining two sides. Each part comprises a thin outer shell of structurally rigid material and an inner lining of sound deadening material, such as polyurethane closed cell foam.

United States Patent [1 1 Derry SOUND BARRIER [76] Inventor: Carl E.Derry, 400 W. Orangethorp,

No. 105 B, Fullerton, Calif. 90632 22 Filed: Dec. 29, 1972 21 Appl. No.:319,379

[52] US. Cl 181/33 G, 181/33 HE, 244/114 B, 256/13.1, 256/24 [51] Int.Cl. B64f l/26, EOlf 15/00 [58] Field of Search 181/30, 33 R, 33 G,181/33 GB, 33 GD, 33 GE, 33 HE; 244/114 R, 114 B; 256/13.l, 24

[56] References Cited UNITED STATES PATENTS 1,825,465 9/1931 MacDonald181/30 2,936,040 5/1960 Rennard 181/33 HE UX 3,382,947 5/1968 Biggs181/30 3,630,310 12/1971 Federer 181/33 HE X 3,656,576 4/1972 Gubela181/33 HE X FOREIGN PATENTS OR APPLICATIONS I 37,063 7/1968 Finland181/33 GB 1 Jan. 8, 1974 1,658,664 12/1970 Germany ..256/13.1

Primary Examiner-Richard B. Wilkinson Assistant Examiner-John F.Gonzales Att0mey-Philip M. Hinderstein [57] ABSTRACT A sound barriercomprising a plurality of hollow, wedge-shaped, energy dissipating cellsmounted in parallel, side-by-side, spaced relationship as inverseactingacoustic horns, first sides of all cells being coplanar. Each of thecells has a plurality of openings in the remaining two sides thereofalong the edges which are adjacent the first side and a plurality ofelongated v openings along the apex defined by the intersection of thetwo sides. Each cell is made in two interlocking parts, one part formingthe first side and the other part forming the remaining two sides. Eachpart comprises a thin outer shell of structurally rigid material and aninner lining of sound deadening material, such as polyurethane closedcell foam.

17 Claims, 6 Drawing Figures PAIENTED 81914 3.783.968

SHEET 10? 2 1 SOUND BARRIER BACKGROUND OF THE INVENTION 1. Field of theInvention.

The present invention relates to sound barriers and, more particularly,to an inexpensive, effectively optically transparent, sound barrierwhich is capable of reflecting, absorbing, and converting sound energyto substantially lower levels ,under all atmospheric conditions.

2. Description of the Prior Art Noise as a product of traffic flowpatterns on urban highways, freeways, and streets is properly becomingof major interest to traffic engineers due to public concern over theincrease in noise pollution and the rapidly increasing numbers ofvehicles on our streets and highways. It is becoming increasingly moreevident that the level of noise one is willing to tolerate on anintermittent level, such as from railroads, low flying aircraft, factorywhistles, etc., is much greater than in those cases where the noisesource is maintained at a steady level with only mild fluctuations. Thisbecomes significant as the pressing need for increasingly complex urbantransportation networks brings freeways and highways near greaternumbers of residential communities. Thus, the traffic noise level whichcan be tolerated while using a freeway going to and from work oftenbecomes intolerable when it is a constant-component of the backgroundnoise level in a residential area.

A recent study performed regarding the attitudes prevailing in severalmajor U. S. cities on the part of urban residents towards various noisesources in the environment supported the proposition that the publicobjects to traffic generated noise more than all other sources combined.It is for this reason that the present invention will be describedprimarily in its application to the reduction of traffic noise onhighways, freeways, and other heavily traveled thoroughfares. However,it will be evident that, and examples will be given how, the presentinvention is applicable to the reduction of noise from other sourcessuch as aircraft, construction, industry, and the like. I

Many attempts have been made to provide sound barriers between heavilytraveled thoroughfares and residential areas, schools, churches,hospitals, offices, and the like. A conventional barrier is in the formof a solid wall which can be in the form of earth or an upright barrier,the latter often made from concrete. In the former case, an effectiveearth barrier may be provided by constructing depressed roadways.Whatever barrier is used, tests have shown that with simple barries,significant noise level reductions are achievable only at extreme Wallheights, in excess of 25 feet, and at higher frequencies, in excess of 1kHz. With lower barrier heights, a maximum attenuation of dB isattainable, due to the influence of defraction effects over a barrier.

Therefore, conventional barriers for traffic noise attenuation haveseveral significant disadvantages. In the first instance, effectivesound reduction is dependent upon barrier height and barrier heights of25 feet or more do not blend aesthetically with the surroundinglandscape. Furthermore, construction costs for high level barriers, suchas earthberms, depressed roadways, and concrete walls, are in the rangeof $50.00 to $500.00 per running foot. Finally, with such barriers, themotorist has the impression that he is captured within a tunnel andtherefore looses his perspective on distance and speed.

One attempt to solve this problem is described in a report entitledKinematic Sound Screen Research Project, Report No. 2, July, 1972,prepared by John Hauskins of Engineering Corporation of America for theArizona Highway Department, Research Division. The Hauskins reportdescribes a sound screen which, at least in theory, goes a long way ineliminating the disadvantages inherent with conventional highway noisebarriers. Such disadvantages are purportedly eliminated by the use of asound barrier incorporating several features. In the first instance, theproposed kinematic sound screen consists of a plurality of Helmholtzresonating chambers which are mounted in parallel, side-by-side, spacedrelationship. By providing each chamber with a triangular cross-sectionand positioning the chambers with first sides coplanar and the remainingtwo sides extending in the same direction, towards a source of sound,the walls of the chambers act as inverse-acting acoustic horns whichfocus the sound energy toward the openings of the Helmholtz resonatingchambers, thus greatly increasing their efficiency. Each chamber has aplurality of openings in each side thereof, at the focal point of theacoustic horns, which act as filters for the incident sound waves. It isstated that on the basis of laboratory experiments, the net effect ofthe attenuation phenomenon will exceed 25 dB, effectively 10 dB downfrom the defracted component of noise reported for conventional solidbarriers.

Such sound barriers have a unique feature in the development of roadsidebarriers for at freeway speeds, it is possible to see through thebarrier via the apertures. In other words, the proposed kinematic soundscreen consists of a series of wedges separated by thin apertures. Anobserver sees only a narrow angle of view through each aperture, but asthe observer moves along a line of travel, the angle of view changes.Thus, an observer traveling at freeway speeds receives overlapping viewsof the field beyond the barrier within the time which the retina of theeye stores an image. By means of a serial strobe effect, the observersees a series of views of the field which he interprets in much the sameway as we view a TV or movie picture.

The use of the exterior walls of the wedge-shaped resonating chambers asmultiple inverse-acting acoustic horns significantly effects the overallperformance of the sound screen. The acoustic horn is essentially atransformer, acting more efficiently than the oscillating mass alonebecause the horn creates a better impedance match between the resonatingchamber and the external air. This means that high pressures are createdin the throat area, causing the vibrating air mass at the neck of theHelmholtz chamber to achieve maximum resonant amplitudes in frequencybands near the resonant frequency of the chamber. The net result of thisair coupling effect is to maximize viscous energy losses for sound wavesentering the Helmholtz chamber.

An integral part of the proposed kinematic sound screen is the Helmholtzresonating chamber. According to the theory developed by Helmholtz, arigid enclosure of volume V connected to the external air mass through asmall opening of effective length L and crosssectional area A has aresonance frequency to which can be expressed by the formula:

( 0 V A/LV,

theoretically effective, problems have been encountered in practicebecause of the use of the Helmhotz resonating chambers. The theoreticaloperation of the Helmholtz resonating chamber is that the air in thecavity opening moves in and out as a unit under fluctuating pressurefrom the external air. The pressure of the air inside the cavity changesas it is alternately compressed and expanded due to movement of the airin the cavity opening. Furthermore, patterns of standing waves aregenerated within the chambers in addition to the oscillating mass of airat the cavity opening. These standing waves generate additionalresonance frequencies which are higher than the fundamental frequency w,and have a significant effect on the frequency range over which dampingoccurs. However, when positioned in the atmosphere, thephenomenon ofoscillating air masses and standing waves within the chamber and at thechamber openings is substantially effected by wind currents and otheratmospheric conditions. For example, not only do the exterior walls ofthe chambers focus the incoming sound energy on the chamber openings,but they also focus wind currents thereon-These wind currents apparentlymodify substantially the pressure of the air inside the resonatorcavities, thereby substantially modifying and'often eliminating or atleast effectively reducing the energy cancellation properties of thechambers. Changes in temperature and humidity also result in changingoperating characteristics of the resonator chambers. Therefore, whilesuch a sound barrier appears highly desirable and practical in theory,it is not as effective in practice.

Finally, the attempts that have been made to generate sound barriers ofthe above described type have used concrete or wood to form the chambersthereby forming a structure which is almost as expensive as conventionalbarriers.

SUMMARY OF THE INVENTION According to the present invention, there isprovided a sound barrier which offers the potential for eliminating notonly the above described disadvantages of conventional highway noisebarriers but also for solving the problems inherent in sound barriersusing Helmholtz resonating chambers and inverse-acting acoustic horns.The present sound barrier is not only relatively inexpensive but iscapable of reflecting, absorbing, and converting sound energy tosubstantially lower levels under all atmospheric conditions. With thepresent sound barrier, effective sound reduction is only slightlydependent upon barrier height and barrier heights of only 6 feet arecapable of achieving attenuations of dB and more. The present soundbarrier blends aesthetically with the surrounding landscape and themotorist is not given the impression that he is captured within a tunnelsince at'freeway speeds, the present sound barrier is visuallytransparent. Finally, the present sound barrier is not effected by windcurrents and other atmospheric conditions and operates as well in thefield as in a testing chamber.

Briefly, the present sound barrier comprises a plurality of hollow,energy dissipating cells, each having a triangular cross-section,mounted in parallel, side-byside, spaced relationship as inverse-actingacoustic horns, first sides of all cells being coplanar or aligned witha continuous, arcuate surface. Because of the spacing between adjacentcells, the barrier appears optically transparent at freeway speeds. Eachof the cells has a plurality of openings in the two remaining sidesthereof along the edges which are adjacent the first side, whichopenings act as side branch filters for the incident sound waves andpermit entrance of the pressure waves into the energy dissipating cells.Furthermore, each cell has a plurality of elongated openings along theapex defined by the intersection of the two sides, which openings directthe incoming sound waves back upon themselves and prevent pressurebuildups within the cells in the presence of air currents. Thus, eachcell acts as a sound energy exchanger, receiving air and sound waves,decreasing the level of the latter, and re-directing both in a definite,prescribed direction.

Each cell is made in two interlocking parts, one part preferably formingthe first side and the other part forming the remaining two sides. Eachpart comprises a thin outer shell of structurally rigid material, suchas aluminum, steel, or plastic, and an inner lining of sound deadeningmaterial, such as polyurethane closed cellv foam or other soundabsorbing material. The cells may be mounted horizontally or verticallyalong a highway, freeway, or other heavily traveled thorough-fare oralong the side of any other noise producing source.

OBJECTS It is therefore an object of the present invention to provide anovel sound barrier.

It is a further object of the present invention to pro vide a highlyeffective, yet inexpensive sound barrier which is capable of reflecting,absorbing, and converting sound energy to substantially lower levelsunder all atmospheric conditions.

It is a still further object of the present invention to provide a soundbarrier which is effectively optically transparent.

It is another object of the present invention to provide' a soundbarrier which may be quickly assembled, disassembled, and retrofittedand which is lightweight and easy to handle.

It is still another object of the present invention to provide a soundbarrier which will blend aesthetically with the surrounding landscape.

Still other objects, features, and attendant advantages of the presentinvention will become apparent to those skilled in the art from areading of the following detailed description of the preferredembodiments constructed in accordance therewith, taken in conjunctionwith the accompanying drawings wherein like numerals designate likeparts in the several figures and wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of aportion of a traffic thoroughfare with the present barrier in positionalong the side thereof;

FIG. 2 is an enlarged perspective view of aportion of the barrier ofFIG. 1;

FIG. 3 is an enlarged cross sectional view taken along the line 33 inFIG. 2;

FIG. 4 is an enlarged cross-sectional view of a portion of the structureof FIG. 3 showing the interlocking connection between the twosubassemblies of the present sound barrier;

FIG. 5 is an exploded view showing the construction of the thin outershells of structurally rigid material of which the sound barrier ofFIGS. l-4 is partially constructed; and

FIG. 6 is a perspective view showing the manner in which the presentsound barrier may be used along the side of an aircraft runway.

DESCRIPTICN OF THE PREFERRED EMBODIMENTS Soundpropagates through air asa series of fluctuations in the local air density,-pressure, andtemperature, as well as disturbances in the positions of air particles.Since each set of fluctuations is repeated at regular intervals, thisform of disturbance can be characterized as wave motion and treated assuch for purposes of description.

It is the magnitude of the fluctuations in pressure that make a soundappear to be loud or soft. At a standard frequency of 1,000 Hz, theminimum audible sound has been determined to be 0.0002 microbar. At theother extreme, the maximum tolerable sound pressure with a frequency of1,000 Hz that can be safely endured is 200 microbars. Since thisrepresents a very broad spectrum, it has proven useful to expressrelative sound pressure in logarithmic units, which also approximatesthe manner in which the human ear judges loudness. The logarithmicmeasure of sound pressure is called the pressure level and is expressedin decibels (dB). The conventional reference used for measuring soundpressure levels has been arbitrarily set at the threshold of hearing at1,000 H2, or 0.0002 microbar. The sound level expressed in decibels thenincreases 20 dB for every 10 times increase in sound.

Tests have shown that sound pressure levels in the range of 70 to 90decibels exist on highways, freeways, and other heavily traveledthoroughfares. On the other hand, recommended sound pressure levels forresidential areas, schools, churches, hospitals, offices, and the likeare in the range of 40 to 50 decibels. This represents a difference inpressure levels between the actual and the desired of approximately 30to 40 dB. However, conventional earthwork and solid wall barrierspositioned on both sides of urban freeways can be expected to giveeffective sound reduction in adjacent areas of dB or less. Barrierheights of feet or more, which obviously do not blend aesthetically withthe surrounding landscape, would be necessary to achieve attenuations of20 dB or more.

Referring now to the drawings and, more particularly, to FIG. 1 thereof,thereis shown a sound barrier, generally designated 10, positionedadjacent the side of a highway, freeway, or other heavily traveledroadway 11 on which cars 12, buses, trucks and the like travel.

It is the function of sound barrier 10 to substantially at- Withreference now to FIGS. 2-5, sound barrier 10 consists of an assembly ofhollow, energy dissipating cells, generally designated 20, each having atriangular cross-section, which are mounted in parallel, side-byside,relationship with a narrow breathing slot 15 therebetween. Each cell 20is identical and includes a first side 21, all of sides 211 typicallybeing coplanar, as

shown in FIGS. 2 and 3. Each cell 21 has two remaining sides 22 and 23which all extend in the same direction, so that all of sides 22 areparallel and all of sides 23 are parallel.

Each cell 20 has a plurality of inlet openings 24 in each of sides 22and 23, openings 24 being spaced along the edges of sides 22 and 23which are adjacent sides 21. Each of cells 20 further has a plurality ofoutlet openings 25 along the leading edge or apex thereof defined by theintersection of sides 22 and 23. As will be described more fullyhereinafter, the size, area, and number of openings 24 and 25 are chosento determine the correct efficiency of sound barrier 10.

According to the preferred embodiment of the present invention, and asshown most clearly in FIGS. 3, 4, and 5, each of cells 20 consist of twoSubassemblies, a rectangular subassembly 26 from which side 21 isconstructed and a triangular subassernbly 27 from which sides 22 and 23are constructed. Subassemblies 26 and 27 preferably comprise thin outershells 28 and 29, respectively, of structurally rigid material, such asfiberglass, plastic, wood, concrete, or a sheet or extruded metal suchas aluminum. Subassemblies 26 and 27 are also preferably lined withsound deadening materials 30 and 31, respectively. Many suitable sounddeadening materials are known but a preferred material is polyurethaneclosed cell foam, foamed in place, and containing a bonding agent toassure a secure bond to shells 28 and 29, respectively.

With reference primarily to FIGS. a and 5, shells 28 and 29 may beextruded continuously in the shape shown and then cut to any desiredlength. Each of shells 28 includes a rectangular back portion 33 and twoside portions 34 and 35 which extend at angles from the side edges ofback portion 33. Shell 28 further comprises flanges 36 and 37 whichextend outwardly from back 33, parallel but spaced from sides 34 and 35,respectively, to define narrow slots 38 and 39. The ends 40 and 41 offlanges 36 and 37 are bent through an angle of 90 so as to extendtowards each other, ends 40 and 41 being coplanar with each other andwith the ends of sides 34 and 35. Finally, approximately twothirds ofthe distance between back 33 and ends 40 and 41, flanges 36 and 37 haveshort dog-legs 42 and 43, respectively, for reasons which will appearmore fully hereinafter.

Shell 29 includes a base portion 44 which is bent through an angle of atthe exact center thereof to form an apex 45 and two sides 46 and $7. Thefree ends 48 and 49 of sides 46 and 47, respectively, are bent throughangles of 30 relative to sides 46 and 47, respectively, so that they areparallel to each other, as shown. The spacing between ends 48 and 49 isexactly equal to the spacing between slots 38 and 39 in shell 28 and thelengths of ends 48 and 69 are slightly smaller than the depths of slots38 and 39. Thus, ends 48 and 49 of shell 29 extend into slots 38 and 39,respectively, of shell 28. In order to retain ends 48 and 49 in slots 38and 39, respectively, sides 46 and 47 of shell 29 include outwardlyprojecting cars 50 and 51, respectively, at

the intersection between sides 46 and 47 and ends 48 and 49,respectively, and inwardly projecting ears 52 and 53, respectively,centrally located along ends 48 and 49. The distance between ear 50 andear 52 and between ear 51 and ear 53 is equal to the distance betweendog-legs 42 and 43 and ends 40 and 41, respectively, of flanges 36 and37, respectively, of shell 28. Thus, when ends 48 and 49 of shell 29 areinserted into slots 38 and 39, respectively, of shell 28, ears 50 and 51will rest on the ends of sides 34 and 35, respectively, and ears 52 and53 will be captured beneath dog-legs 42 and 43, respectively. Theresiliency within the material from which shell '28 is formed willpermit a slight deflection of flanges 36 and 37 as ears 52 and 53,respectively, pass between flanges 36 and 37 and sides 34 and 35,respectively.

Each of shells 29 further. includes flanges 54 and 55 which extendinwardly from the inner surfaces of sides 46 and 47, respectively,thereof. Flanges 54 and 55 are coplanar and are spaced from ends 40 and41, respectively, of shell 28 by an amount which is slightly greaterthan the desired width of inlet openings 24. The ends 56 and 57 offlanges 54 and 55, respectively, are bent through an angle of 60 so asto extend parallel to sides 46 and 47, respectively, towards apex 45.The spacing between ends 56 and 57 and sides 46 and 47, respectively, aswell as the spacing between ends 40 and 41 and back 33 is determined bythe thickness desired for sound deadening material 30 and 31,respectively.

Finally, each of shells 29 has a plurality of elongated openings 24 ineach ofsides 46 and 47, between ears 50 and 51 and flanges 54 and 55,respectively. The length, width, location, and spacing between openings24 will be discussed more fully hereinafter. At the present time,openings are not formed in shell29.

Ends 40 and 41 of flanges 36 and 37, respectively, of

Y shell 28 and ends 56 and 57 of flanges 54 and 55, re-

spectively, of shell 29 define the areas of shells 28 and 29 which areto be lined with sound deadening materials and 31, respectively. Asmentioned previously, any suitable sound deadening material may be usedal though a polyurethane closed cell foam is highly effective and mostdesirable. A polyurethane closed cell foam may be applied to shells 28and 29 in the manner described, in copending U. 5. Patent ApplicationSer. No. 181,703 filed Sept. 21,1971, by Carl E. Derry and William A.Childs for Thermally Insulated Building Material and Method and Meansfor the Manufacture Thereof. For example, and as described more fully insuch application, shells 28 and 29 may be positioned on their backs,with the sides to be lined with foam facing upwardly, and passed beneatha plurality of spray nozzles which inject a polyurethane foam, in liquidform, thereon. Shells 28 and 29 would then be passed beneath conveyorbelts which permit rising of the foam to the desired shape.

In the case of shell 28, a flat conveyor belt resting on top of ends and41 of flanges 36 and 37, respectively, will permit the foam to fill thearea defined by back 33, flanges 36 and 37, and ends 40 and 41 thereof.In the case of shell 29, a triangular conveyor belt resting on top ofends 56 and 57 of flanges 54 and 55, respectively, and having a suitablecross-sectional shape would be required to permit the foam to line theinner surfaces of sides 46 and 47,from flange 54 to flange 55.

Reference to the above-mentioned copending Patent Application may be hadfor a fuller explanation of the foaming process. In any event, the foamwould have a suitable bonding agent included therein so as to form arigid, unitary structure with shells 28 and 29.

It should be evident that using the above described manufacturingprocedure, it would not be possible to initially form outlet openings 25in apex 45 of each of cells 20 since to do so would permit escape of theliquid foam of which sound deadening material 31 is. formed. Therefore,openings 25 would have to be cut through apex 45 of shell 29 after thefoaming step is completed. This may be achieved in any suitable manner.

After the foaming step is completed and subassembli es 26 and 27 arecompletely formed, they may be connected together in the mannerdescribed previously by extending ends 48.and 49 of subassembly 27 intoslots 38 and 39 in subassembly 26. Thereafter, cells 20 may be installedin any suitable manner. For example, if cells 20 are to be used along aroadway 1 1, as shown in FIG. 1, cells 20 may be formed in 4 or 6 footlengths and mountee a short distance from the side of roadway 11. Thecells 20 may also be stacked, one above the other, to any desiredheight. A suitable mounting technique would be to support, in anysuitable manner, first and second horizontal, vertically spaced angles13 and 14 along the side of roadway 11 with first sides 16 and 17 ofangles 13 and 14, respectively, coplanar and with second sides 18 and 19of angles 13 and 14, respec tively, parallel and spaced by an amountslightly greater than the length of cells 20. Thereafter, cells 20 maybe positioned between angles 13 and 14, with sides 21 thereof restingagainst sides 16 and 17 of angles 13 and 14, respectively. A pluralityof sheet metal screws 8 may then be extended through a plurality ofholes 9 formed in sides 16 and 17 of angles 13 and 14, respectively, andinto backs 33 of sides 21 of cells 20. This simple procedure permitsrapid and efficient assembly of barrier 10 along the side of roadway 11.Also, side 18 of angle 13 serves as a cover to prevent various forms ofenvironmental precipitation from getting into cells 20. On the otherhand, to the extent that such precipitation finds its way into cells 20,it will be drained therefrom via the space between the bottom of cells20 and side 19 of angle 14. I

In operation, and with reference to FIGS. 2 and 3, the improvement innoise attenuation performance of sound barrier 10 is attributable to theinteraction of several phenomena. In the first instance, the exteriorwalls of sides 22 and 23 of cells 20 act as multiple inverse-actingacoustic horns which focus the sound en.- ergy toward openings 24 incells 20 and 21. More specifically, sound or noise from a fixed ormoving source produces successive waves 58 of compressed air whichadvance toward barrier 10. These waves undergo further compression asthey travel along sides 22 and 23 between each set of cells 20. In otherwords, as a first wave enters the constricting area just beyond apices45, there will be some scattering of energy. But if another wavefrontenters the constricting area before the first has an opportunity todissipate, then the first wave will. be forced into an area ofincreasing pressure until it reaches openings 24in cells 20. At thispoint, large amplitude vibrations of the air mass adjacent openings 24are set up, which vibrations are damped by theremaining structure to bedescribed immediately hereinafter. However, it is significant to notethat the acoustic horns are essentially transformers, acting moreefiiciently than the oscillating mass alone because the horn cre- Thecompressed air which serves as the media for sound energy propagation isnow diverted from a high pressure zone, at each opening 24, into theadjacent cells 20, which are at a lower pressure, rapidly expandingwithin cells 20, thereby dissipating additional energy. The opposingwaves 59 of compressed air flowing within each chamber 20 now generateturbulent air swirls which produce additional energy dissipation. Theswirling air patterns within each cell 20 impact against sound deadeningmaterial 30 and 31, dissipating still additional sound energy.

Additional wavefronts 59 of compressed air entering cells 20 recompressthe preceeding wavefronts, producing additional energy losses. Thus, theopenings in sides 22 and 23 of cells 20 are a second phenomenon whichcontributes to the improvement in noise attenuation performance of soundbarrier 10.

The compressed, expanded, and recompressed sound waves within each cell20 now respirate through outlet openings 25 in apices 45 of cells 20 toa low pressure zone immediately in front of each apex 45. Morespecifically, when the successive waves 58 of compressed air reachapices 45 of cells 20, they are broken up and directed along sides 22and 23, betweeneach pair of cells 20. This has the effect of creating apartial vacuum adjacent each apex 45, which partial vacuum draws the airwithin cells 20 out through openings 25. The compressed air which servesas the media for sound energy propagation is now again diverted from ahigh pressure zone, within cells 20, adjacent openings 25, back into theatmosphere, which is at a significantly lower pressure, rapidlyexpanding and dissipating additional energy. Furthermore, the wavefronts60 exiting from openings 25 propagate in a direction opposed to theincoming waves 58 which, by molecular impact, cause additional energydissipation.

In other words, the first wavefronts 58 impinging upon sound barrier 10are substantially reduced in en ergy level and a substantial portion ofthe remaining energy level is directed back upon the incoming soundenergy, thereby decreasing the level of such sound energy before it evenreaches barrier 16 The new wavefronts, which have now been decreased inmagnitude, are recirculated through cells 20, as described previously,-

with corresponding energy losses, and a substantial portion of theremaining energy is then directed back against successive wavefronts58., This phenomenon, integrated together, produces the desiredsubstantial lowering of sound energy levels.

It should be particularly noted that in theory and in practice, verylittle of the incident sound energy is transmitted through slots betweencells 20. Many factors effect the ratio of the power transmitted to theinput power, such as the area of inlet openings 24, the characteristicacoustic reactance of cells 20, the characteristic acoustic resistanceof cells 20, the volumeof cells 20, and the like. it has been found thatas long as the width of slots 15 is small relative to the width of sides21 of cells 20, very little of the incident sound energy is transmittedthrough slots 15. By way of example, each of sides 21, 22, and 23 ofcells may be approximately 4 inches wide and siots 15 may be oneeighthinch wide. Openings 24 may be 6 inches long and one-quarter inch wideand spaced longitudinally by 1 /2 inches. Such a configuration has beenfound to pro duce superior operating characteristics.

On the other hand, slots 15 are necessary since they permit aircirculation between each pair of cells 20, so as to prevent unwanted aircirculation or air pressure build-up near inlet openings 24. Slots 15also subdue diaphragm-like vibrations of the rear walls 33 of cells 20,which otherwise would act as secondary noise sources.

The relationship between the area of openings 25 to the area of openings24 significantly effects the operation of cells 26. More specifically,since openings 25 are intended to be outlet openings to permit airpressures within cell 20 to respirate, the combined area of inletopenings 24 should be large compared to the combined area of outletopenings 25. Also, if outlet openings 25 were too large, the turbulentair swirls which produce energy dissipation within cells 2i would beinhibited. By way of example, outlet openings 25 may be 6 inches long bythree thirty-second inches wide and may be spaced longitudinally by 1foot. With such dimensions, the ratio of the combined area of inletopenings 24 to the combined area of outlet openings 25 is 10.77 to 1 andthis ratio has been found through tests to be highly effective. In otherwords, the ratio of the combined area of inlet openings 24 in each cell20 to the combined area of outlet openings 25 should be at leastapproximately 10 to 1.

It can therefore be seen that in accordance with the present invention,there is provided a sound barrier 10 which offers the potential foreliminating not only the disadvantages of conventional highway noisebarriers but also for solving the problems inherent in sound barriersusing Helmholtz resonating chambers and inverseacting acoustic horns.Sound barrier it) is not only inexpensive, but is capable of reflecting,absorbing, and converting sound energy to substantially lower levelsunder all atmospheric conditions. With sound barrier 10, effective soundreduction is only slightly dependent upon barrier height and barrierheights of only 6 feet are capable of achieving attenuations of 20 dBand more. Sound barrier M) blends aesthetically with the surroundinglandscape and a motorist in vehicle 12 is not given the impression thathe is captured within a tunnel since at freeway speeds, sound barrier 10is visually transparent.

Of greatest significance, sound barrier 10 is not effected by windcurrents and other atmospheric conditions and operates as well in thefield as in a testing chamber. The wind currents which are focused bywalls 22 and 23 towards openings 24 in cells 20 respirate not onlythrough slots 15 but also through cells 2% via inlet and outlet openings24 and 25, respectively. Thus, these wind currents do not modify orreduce the energy cancellation properties of barrier 10. Rather, eachcell 20 acts as a sound energy exchanger, receiving air and sound wavesand redirecting them, the latter in decreased form, in a definite,prescribed direction. Cells 20 are thus distinguishable from Helmholtzchambers which function only as resonators.

in the embodiment of FIG. 1, cells 20 are shown having a length ofapproximately 4 feet and as being mounted vertically along the side ofroadway 11. However, it will be apparent to those skilled in the artthat other configurations are possible. For example, and with referenceto FIG. 6, there is shown a sound barrier, generally designated 70,positioned adjacent the 1 side of an airport runway 71 on which aircraft72 take off and land. Barrier 70 consists of a plurality of hollow,wedge-shaped, energy dissipating cells 72 which are identical inconstruction and operation to cells 20. 5 However, each of cells 73 isquite long and cells 73 are mounted horizontally in parallel,side-by-side, spaced relationship along the sides of runway 71. Cells 73may be mounted with first sides coplanar or may be mounted with firstsides positioned along an arcuate supporting surface 74. This latterconfiguration has the advantage of redirecting some of the incidentsound energy upward and not back towards aircraft 72. Otherconfigurations and orientations of energy dissipating cells constructedin accordance with the teachings of I5 the present invention will beapparent to those skilled in the art.

While the invention has been described with respect to the preferredphysical embodiments'constructed in accordance therewith, it will beapparent to those skilled in the art that various modifications andimprovement may be made without departing from the scope and spirit ofthe invention. Accordingly, it is to be understood that the invention isnot to be limited by the specific illustrative embodiments, but only bythe scope of the appended claims.

I claim:

1. A sound barrier comprising:

a plurality of hollow, energy dissipating cells, each having atriangular cross-section, mounted in parallel, side-by-side, spacedrelationship with first sides of all of said cells being coplanar oraligned with a continuous, arcuate surface and the remaining two sidesof all of said cells extending in the same direction, towards a sourceof sound;

each of said cells having a plurality of inlet openings in each of saidremaining two sides thereof, said inlet openings being spaced along theedges of said two sides which are adjacent said first side; 40

each of said cells further having at least one elongated outlet openingalong the apex thereof defined by the intersection of said two sides,the combined area of said plurality of inlet openings in each cell beingsubstantially greater than the area of said elongated outlet opening ineach cell.

2. A sound barrier according to claim 1 wherein the spacing betweenadjacent cells is substantially smaller than the width of said firstsides thereof.

3. A sound barrier according to claim 1 wherein the lengths of saidinlet openings are at least four times greater than the spacing betweenadjacent openings.

4. A sound barrier according to claim 1 wherein the 1 combined area ofsaid plurality of inlet openings in each cell is approximately ten timesthe area of said outer shell is made from aluminum.

9. A sound barrier according to claim 8 wherein said sound deadeningmaterial is polyurethane closed cell foam.

10. A sound barrier according to claim 6 wherein said sound deadeningmaterial is polyurethane closed cell foam.

11. A sound barrier according to claim 1 wherein each of said cellsconsists of two subassemblies, a first generally rectangular subassemblyfrom which said first side is formed and a'second generally triangularsubassembly from which said remaining two sides are formed, said firstand second subassemblies including means for forming an interlockingconnection therebetween.

12. A sound barrier according to claim 11 wherein each of saidsubassemblies comprises a thin outer shell of structurally rigidmaterial and an inner lining of sound deadening material. 13. A soundbarrier according to claim 12 said shell of said first subassemblycomprises:

a rectangular back portion;

two perpendicular side portions; and

first and second flanges which extend outwardly from said back portion,parallel to and spaced from said side portions to define narrow slotstherebetween; and wherein said shell of said second subassemblycomprises:

a base portion which is bent through an angle of at the exact centerthereof to form said apex and said two remaining sides, the free ends ofsaid sides being bent through angles of 30 so as to be parallel to eachother, the spacing between said ends being exactly equal .to the spacingbetween said slots in said first subassembly whereby said ends extendinto said slots.

14. A sound barrier according to claim 13 wherein I said means forforming an interlocking connection between said subassemblies comprises:

a dog-leg in said flanges of said first subassembly;

an outwardly projecting ear at each intersection between said sides andsaid ends of said second subassembly; and

an inwardly projecting ear centrally located along each of said ends ofsaid second subassembly, the distance between each outwardly projectingear and each inwardly projecting ear being equal to the distance betweensaid dog-legs and the ends of said flanges whereby said outwardlyprojecting ears rest on the ends of said side portions of said firstsubassembly and said inwardly projection ears afe captured beneath saiddog-legs in said flanges of said first subassembly.

15. A sound barrier according to claim 13 wherein said lining of sounddeadening material of said first subassembly extends between said firstand second flanges thereof.

16. A sound barrier according to claim 13 wherein said shell of saidsecond subassembly further comprises:

first and second flanges extending inwardly from the inner surfaces ofsaid sides thereof, said flanges being coplanar and spaced from saidends of said sides by an amount which is slightly greater than the widthof said inlet openings, said lining of sound deadening material of saidsecond subassembly extending along the inner surfaces of said sides ofsaid shell, between said flanges thereof.

17. A sound barrier according to claim 16 wherein said inlet openingsextend between said first and second flanges and the adjacent ends ofsaid sides of said base portion of said shell of said secondsubassembly. l

wherein

1. A sound barrier comprising: a plurality of hollow, energy dissipatingcells, each having a triangular cross-section, mounted in parallel,side-by-side, spaced relationship with first sides of all of said cellsbeing coplanar or aligned with a continuous, arcuate surface and theremaining two sides of all of said cells extending in the samedirection, towards a source of sound; each of said cells having aplurality of inlet openings in each of said remaining two sides thereof,said inlet openings being spaced along the edges of said two sides whichare adjacent said first side; each of said cells further having at leastone elongated outlet opening along the apex thereof defined by theintersection of said two sides, the combined area of said plurality ofinlet openings in each cell being substantially greater than the area ofsaid elongated outlet opening in each cell.
 2. A sound barrier accordingto claim 1 wherein the spacing between adjacent cells is substantiallysmaller than the width of said first sides thereof.
 3. A sound barrieraccording to claim 1 wherein the lengths of said inlet openings are atleast four times greater than the spacing between adjacent openings. 4.A sound barrier according to claim 1 wherein the combined area of saidplurality of inlet openings in each cell is approximately ten times thearea of said elongated outlet opening in each cell.
 5. A sound barrieraccording to claim 4 wherein each of said cells has a plurality of saidoutlet openings spaced along said apex thereof.
 6. A sound barrieraccording to claim 1 wherein each of said cells comprises: a thin outershell of structurally rigid material and an inner lining of sounddeadening material.
 7. A sound barrier according to claim 6 wherein saidouter shell is made from sheet metal.
 8. A sound barrier according toclaim 6 wherein said outer shell is made from aluminum.
 9. A soundbarrier according to claim 8 wherein said sound deadening material ispolyurethane closed cell foam.
 10. A sound barrier according to claim 6wherein said sound deadening material is polyurethane closed cell foam.11. A sound barrier according to claim 1 wherein each of said cellsconsists of two subassemblies, a first generally rectangular subAssemblyfrom which said first side is formed and a second generally triangularsubassembly from which said remaining two sides are formed, said firstand second subassemblies including means for forming an interlockingconnection therebetween.
 12. A sound barrier according to claim 11wherein each of said subassemblies comprises: a thin outer shell ofstructurally rigid material and an inner lining of sound deadeningmaterial.
 13. A sound barrier according to claim 12 wherein said shellof said first subassembly comprises: a rectangular back portion; twoperpendicular side portions; and first and second flanges which extendoutwardly from said back portion, parallel to and spaced from said sideportions to define narrow slots therebetween; and wherein said shell ofsaid second subassembly comprises: a base portion which is bent throughan angle of 120* at the exact center thereof to form said apex and saidtwo remaining sides, the free ends of said sides being bent throughangles of 30* so as to be parallel to each other, the spacing betweensaid ends being exactly equal to the spacing between said slots in saidfirst subassembly whereby said ends extend into said slots.
 14. A soundbarrier according to claim 13 wherein said means for forming aninterlocking connection between said subassemblies comprises: a dog-legin said flanges of said first subassembly; an outwardly projecting earat each intersection between said sides and said ends of said secondsubassembly; and an inwardly projecting ear centrally located along eachof said ends of said second subassembly, the distance between eachoutwardly projecting ear and each inwardly projecting ear being equal tothe distance between said dog-legs and the ends of said flanges wherebysaid outwardly projecting ears rest on the ends of said side portions ofsaid first subassembly and said inwardly projection ears are capturedbeneath said dog-legs in said flanges of said first subassembly.
 15. Asound barrier according to claim 13 wherein said lining of sounddeadening material of said first subassembly extends between said firstand second flanges thereof.
 16. A sound barrier according to claim 13wherein said shell of said second subassembly further comprises: firstand second flanges extending inwardly from the inner surfaces of saidsides thereof, said flanges being coplanar and spaced from said ends ofsaid sides by an amount which is slightly greater than the width of saidinlet openings, said lining of sound deadening material of said secondsubassembly extending along the inner surfaces of said sides of saidshell, between said flanges thereof.
 17. A sound barrier according toclaim 16 wherein said inlet openings extend between said first andsecond flanges and the adjacent ends of said sides of said base portionof said shell of said second subassembly.